1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device including grinding a semiconductor wafer after stacking semiconductor chips on the semiconductor wafer.
2. Description of the Related Art
With miniaturization and sophistication of electronic equipment, chip-on-chip (CoC) semiconductor devices with a plurality of semiconductor chips stacked on top of one another have recently been developed. JP2012-209449A discloses a chip-on-wafer (CoW) method that stacks semiconductor chips as individual pieces on a base wafer to form chip stacks and then separates the base wafer into individual pieces to obtain chip stacks. The chip stacks as individual pieces are mounted on a wiring board.
FIGS. 17 to 28 of JP2012-209449A show a method of manufacturing a semiconductor package. According to the manufacturing method, a semiconductor substrate is first prepared in which a plurality of portions, that serve as IF chips, are arrayed. A plurality of memory chips are then flip-chip mounted on the semiconductor substrate for each of the portions that serve as IF chips. With this operation, chip stacks having a plurality of semiconductor chips stacked on top of one another are formed. A groove is formed in the semiconductor substrate along a dicing line through half-cut dicing using a dicing blade. A support substrate is attached to memory chips at the top layer mounted on the semiconductor substrate via an adhesive layer. One face of the semiconductor substrate which is on the opposite side from a face with the support substrate, i.e., a face on the opposite side from a face with the groove formed through halt-cut dicing is ground (back-ground). At this time, the semiconductor substrate is thinned to reach a bottom of the groove formed through half-cut dicing. With this operation, the semiconductor substrate is divided into chip stacks.
Next, the chip stacks are mounted on a mother wiring board. Solder balls that serve as external terminals are arranged on the mother wiring board. Next, the mother wiring board is cut so that it is divided into individual semiconductor packages.
The present inventor has found shat thinning a semiconductor substrate (semiconductor wafer) through back-grinding after flip-chip mounting a plurality of memory chips on the semiconductor substrate leads to the problem below.
When memory chips are mounted on a plurality of IF chips of a semiconductor substrate, semiconductor chips may be mounted on only some of the IF chips. For example, if there is a defective IF chip, a semiconductor chip will be not mounted on the defective IF chip. In this case, a large void is created at a portion on the semiconductor substrate where a semiconductor chip is not mounted. When one face of the semiconductor substrate is ground through back-grinding in the presence of this void, there is variation in the load on the semiconductor substrate. As a result, a part of a semiconductor chip may be damaged (a chip crack may occur) or there may be variation in the thickness of the semiconductor substrate after grinding. There is thus a need for an improved method of manufacturing a semiconductor device.